THREDDS folks,
Just in case folks want to see an example of the kind of application
that Tom & Co. have developed using these OGC standards, check out
their very cool and powerful (although awkwardly named) "Geo Data
Portal", which allows you to compute statistics from historical and
climate model projections over a geographic region you specify (e.g.
what do the IPCC models predict the precipitation will look like in my
county under the B1 scenario in 2050)
Here's a video showing how it works:
http://cida.usgs.gov/climate/screencast/
and the application is at
http://cida.usgs.gov/climate/gdp
Using WMS, WCS, OPeNDAP + CF, and tied together with WPS.
Cool stuff.
-Rich
On Mon, Jul 2, 2012 at 1:55 AM, Tom Kunicki <tkunicki@xxxxxxxx> wrote:
>
> On (C) I definitely concur. I am not against simplicity and HTTP GET
> requests. I just want to make sure that the approach is discussed and that
> one doesn't fall into the trap of believing HTTP GET is a panacea of
> simplicity. These URLs that have been posted are pretty complex and aren't
> the kinds of things that anyone but expert users will be crafting by hand.
> There will be a client implementation in front of them and they will need to
> be updated if the server processing API behind them changes. In this case,
> the client implementation will have to change in tandem with the server side
> processing API. This will be true regardless of whether the request is GET,
> POST, PUT, etc. One benefit of GET is an embeddable link, to my knowledge
> this isn't easily done with POST or PUT.
>
> Our group uses WPS. We had issues with some holes with some implementation
> and the specification so we made a choice to join on to the WPS 2.0 SWG.
>
> There are advantages to the WPS specification. Implementations can list a
> set of supported operations and processes using the GetCapabilities request
> (a GET or POST, we use GET). Each process can be queried for it's API
> including supported inputs and outputs (name, mime-type and schema if xml)
> using a DescribeProcess request (GET or POST, we use GET). If you know the
> arguments and types you can parse the DescribeProcess response and
> automatically generate a UI. We have implemented this in JavaScript for our
> Web-based brokering services. There are python clients as well as an Arc
> plugin in-progress (completed?) by ERSI and 52n, also a qGIS plugin among
> others. Processes can be executed with an Execute request (a GET or POST
> request, we use POST). POST for us because we deal with some pretty complex
> inputs (WFS calls with server side geometry filtering by reference to a GET
> or POST request; or Base64 encoded shapefiles sent in-line). These would
> bump us into some URL len
> gth restrictions we have dealt with in the past. We don't have to use these
> complex inputs but since WPS offers this flexibility we are happy to leverage
> it. When we execute processes we have the options to execute them
> synchronously or asynchronously (and an implementation can control these
> options by advertising them per process.) We can query the executing process
> for it's completion state (POST, don't know if GET is possible as I haven't
> looked into it). We can request executions results in-line with the response
> or by reference. We provide inputs to WPS calls as the results of other WPS
> calls. WPS processing implementations can be complex or simple. Given our
> use cases we made an architectural decision to leverage some of the more
> advanced components of the specification. We've developed some complex
> processing that does some cool and useful things that we are able to leverage
> in other projects and share with other groups. With our processing endpoints
> we can a
> dd a process and have it automatically be displayed in our UIs. One of the
> benefits of WPS was processing end-points became self-documenting.
>
> Now, the WPS execute by GET is pretty tricky as it requires so double URL
> encoding. We are happy using POST and didn't delve too much into GET. If
> there was a need and someone wanted to look at this with me (ahem, Roy?) I
> would be more that happy to submit some change requests to simplify the
> specification for some use cases. In my experience with the OGC standards
> almost everything can be done with GET, it's when you get into the outlying
> use cases you have to represent your requests with POST.
>
> WPS is an OGC specification. I think the last 2 words of the previous
> sentence instantly turn people off. But there's some real value to the work
> that's been done. We've used it as a thin wrapper on process execution. Our
> initial cut at processing involved using simple GET-based services. We found
> we had to generate a whole suite of utility/supporting GET-based services
> relying on clients to perform operations with correct ordering. The
> architecture was becoming difficult to maintain and document. A large number
> of tasks have now been implemented with the OGC standards suite and available
> standards implementations. This has saved our group a lot of development
> time and in turn taxpayer dollars.
>
> Tom Kunicki
> Center for Integrated Data Analytics
> U.S. Geological Survey
> 8505 Research Way
> Middleton, WI 53562
>
>
>
> On Jul 1, 2012, at 11:34 PM, Gerry Creager wrote:
>
>> Roy,
>>
>> That's a good explanation, and one I can live with. However, I also agree
>> with Jeff's later comments, that A) in general, the same interpreter can
>> handle GET and POST, and B) file uploads can't happen with a GET.
>>
>> And, most important: C) KISS is a good mantra.
>>
>> I'll sit back and listen to the debate again.
>>
>> gerry
>>
>> On Sun, Jul 1, 2012 at 3:13 PM, Roy Mendelssohn <roy.mendelssohn@xxxxxxxx>
>> wrote:
>> BTW - a discussion we have been having around these parts is can you do
>> enough in the way of server-side functions without a POST (ie the URL
>> defines the function). That is why I would like to hear more from people
>> who are running F-TDS and GDS - how many requests do they get for server
>> side functions, but is the usual response time and download for these
>> request, how large are the usual expressions? And then contrast it with a
>> WPS or WCPS approach. I clearly believe in one approach, but I would
>> welcome people who are using some of these other approaches to describe what
>> they have done, the benefits of doing things that way, and what it means for
>> a client.
>>
>> Thanks,
>>
>> -Roy
>>
>> On Jul 1, 2012, at 11:25 AM, Dennis Heimbigner wrote:
>>
>> > Roy-
>> >
>> > > ... One comment. I think you misunderstood my point about
>> > > Matlab and R. I am not interested in Matlab specific
>> > > implementations. The point was because the URL completely
>> > > defines the request, I can implement scripts in any application
>> > > that can send an URL and receive a file in terms of functions
>> > > built-in to that application - that is my clients do not break as
>> > > the application or operating system change.
>> >
>> > Not quite sure I understand. This phrase "...receive a file in
>> > terms of functions built-in to that application" sounds
>> > like you are creating an association between functions defined
>> > on the client side and functions defined on the server side.
>> > Can you elaborate?
>> >
>> > > Why I strongly prefer, if it is at all reasonable, services that
>> > > only use GET, not POST.
>> >
>> > Again, that is only possible if you keep your requests
>> > short enough to not violate the URL length restrictions.
>> >
>> > =Dennis Heimbigner
>> > Unidata
>> >
>> >
>> >
>> > Roy Mendelssohn wrote:
>> >> Hi Dennis:
>> >> Thanks. One comment. I think you misunderstood my point about Matlab
>> >> and R. I am not interested in Matlab specific implementations. The
>> >> point was because the URL completely defines the request, I can implement
>> >> scripts in any application that can send an URL and receive a file in
>> >> terms of functions built-in to that application - that is my clients do
>> >> not break as the application or operating system change.
>> >> While I understand why this occurred, a few years ago we had straight
>> >> OPeNDAP implementations. We had a lot of users using scripts we
>> >> developed for Matlab, running under Windows. Due to updates in both
>> >> Windows and Matlab, the OPeNDAP files for Windows stopped working (at
>> >> least for Matlab). We had a lot of users that were left stranded and
>> >> stranded for quite a long time. Developing and maintaining clients,
>> >> particularly clients that are working within an application for which you
>> >> have to write code, very quickly becomes a non-trivial exercise.
>> >> Since we switched to a service where the URL completely defines the
>> >> request, our Matlab and R scripts have survived quite nicely any number
>> >> of updates both to the applications themselves and to the operating
>> >> systems. That is because the clients now only use functions built into
>> >> the applications.
>> >> Why I strongly prefer, if it is at all reasonable, services that only use
>> >> GET, not POST.
>> >> -Roy
>> >> On Jun 28, 2012, at 1:03 PM, Dennis Heimbigner wrote:
>> >>>> I am old and slow, but suppose I am in OpeNDAP, are you proposing
>> >>>> to separate say constraint expressions and server-side function
>> >>>> requests basically the same (ie I just scan what is after each
>> >>>> comma) or do you propose some method that signifies in the URL
>> >>>> that what follows is an expression? In F-TDS and GDS the form of
>> >>>> the URL is:
>> >>> First, I am proposing to subsume DAP constraints.
>> >>> Second, I am proposing, like DAP, to put the expressions
>> >>> in the query part of the URL (i.e. after the '?').
>> >>>
>> >>>> http://machine:port/thredds/dodsC/dataset_expr_{dataset2,dataset3,...}{expression1;expression2;...}.URLsuffix?constraint
>> >>> So, I would rewrite this as something more-or-less like this:
>> >>> http://machine.../dataset?expression1,expression2,...
>> >>> Where the expressions would include the references to dataset2, dataset3,
>> >>> and the constraint.
>> >>>
>> >>>> BTW, the reason I have asked about the experience of people who
>> >>>> are using F-TDS and GDS on whether synchronous requests can cover
>> >>>> the large majority of cases, is because I am very partial to
>> >>>> systems where the URL completely defines the request, and hence
>> >>>> essentially use GET as the verb.
>> >>> The synchronous/asynchronous issue is, for me, a separable issue.
>> >>> I should note that GET has a limit on the size of URLS, so
>> >>> there needs to be ways to deal with that. Two possibilities are
>> >>> 1) use POST or PUT, or 2) provide a way to upload a long expression
>> >>> in parts USING multiple GETs.
>> >>>
>> >>>> The reason for this is long
>> >>>> experience. where client code has broken with changes in
>> >>>> operating system and/or application, fixes were slow in coming,
>> >>>> so many users were left with nothing working. In a system where
>> >>>> the URL completely defined the request, say ERDDAP, in Matlab:
>> >>>>
>> >>>>>> link='http://coastwatch.pfeg.noaa.gov/erddap/griddap/erdBAsstamday.mat?sst[(2010-01-16T12:00:00Z):1:(2010-01-16T12:00:00Z)][(0.0):1:(0.0)][(30):1:(50.0)][(220):1:(240.0)]';
>> >>>>>> F=urlwrite(link,'cwatch.mat');
>> >>>>>>
>> >>>> Will get the related file, and the entire command is in Matlab,
>> >>>> no extra code required. The same in R is:
>> >>>>
>> >>>>>> download.file(url="http://coastwatch.pfeg.noaa.gov/erddap/griddap/erdBAsstamday.nc?sst[(2010-01-16T12:00:00Z):1:(2010-01-16T12:00:00Z)][(0.0):1:(0.0)][(30):1:(50.0)][(220):1:(240.0)]",
>> >>>>>> destfile="AGssta.nc",mode='wb')
>> >>>>>>
>> >>>> again, "download.file" is an R command.
>> >>> I think that we do not want to be R/MATLAB specific
>> >>> in a proposal to put stuff in URLs. I would rather
>> >>> propose to allow uploading of R/MATLAB scripts to serve
>> >>> as additional, user-defined functions.
>> >>>
>> >>> I would prefer to
>> >>>> maintain this simplicity and cover 80% of the cases if possible,
>> >>>> than cover the rest but where more complex, application specific
>> >>>> code would have to be developed and maintained.
>> >>> Agreed. However my assumption is the the output of any function that
>> >>> is not assigned to a single-assignment variable will be returned as part
>> >>> of the response; but other ways of specifying this are possible within
>> >>> the functional framework I am proposing.
>> >>>
>> >>> =Dennis Heimbigner
>> >>> Unidata
>> >> **********************
>> >> "The contents of this message do not reflect any position of the U.S.
>> >> Government or NOAA."
>> >> **********************
>> >> Roy Mendelssohn
>> >> Supervisory Operations Research Analyst
>> >> NOAA/NMFS
>> >> Environmental Research Division
>> >> Southwest Fisheries Science Center
>> >> 1352 Lighthouse Avenue
>> >> Pacific Grove, CA 93950-2097
>> >> e-mail: Roy.Mendelssohn@xxxxxxxx (Note new e-mail address)
>> >> voice: (831)-648-9029
>> >> fax: (831)-648-8440
>> >> www: http://www.pfeg.noaa.gov/
>> >> "Old age and treachery will overcome youth and skill."
>> >> "From those who have been given much, much will be expected" "the arc of
>> >> the moral universe is long, but it bends toward justice" -MLK Jr.
>>
>> **********************
>> "The contents of this message do not reflect any position of the U.S.
>> Government or NOAA."
>> **********************
>> Roy Mendelssohn
>> Supervisory Operations Research Analyst
>> NOAA/NMFS
>> Environmental Research Division
>> Southwest Fisheries Science Center
>> 1352 Lighthouse Avenue
>> Pacific Grove, CA 93950-2097
>>
>> e-mail: Roy.Mendelssohn@xxxxxxxx (Note new e-mail address)
>> voice: (831)-648-9029
>> fax: (831)-648-8440
>> www: http://www.pfeg.noaa.gov/
>>
>> "Old age and treachery will overcome youth and skill."
>> "From those who have been given much, much will be expected"
>> "the arc of the moral universe is long, but it bends toward justice" -MLK Jr.
>>
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